Campylobacter jejuni and coli have now been recognized as among the most frequent causes of bacterial enteritis in both developed and developing countries. Little is known about the manner by which these organisms cause disease, although there are data that support both toxic and invasion-- mediated pathogenic mechanisms. Our work has focused on examination of the molecular properties of these organisms and their relationship to the virulence factors associated with disease production. Both the ultrastructural and physiologic properties of Campylobacter interaction with cultured human epithelial cell lines have been examined in efforts to assess the potential invasive properties of the organism. Oligonucleotide probes, specific antibodies, and enzymatic assays have been employed to identify potential cholera toxin-like molecules that might be involved in the production of diarrheal disease. Monoclonal antibodies to surface proteins have been produced and are being used to identify molecules that might be involved in adherence, colonization, and invasion. These antibodies are also being used to screen recombinant Campylobacter DNA libraries for the purpose of determining gene structure and investigating genetic regulation.